Silicate minerals

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of rock-forming minerals and make up approximately 90 percent of the Earth's crust.^[1] They are classified based on the structure of their silicate groups, which contain different ratios of silicon and oxygen.

Nesosilicates or orthosilicates

Basic (ortho-)silicate anion structure

Nesosilicate specimens at the Museum of Geology in South Dakota

Nesosilicates (from Greek νῆσος nēsos, island), or orthosilicates, have the orthosilicate ion, which constitute isolated (insular) [SiO₄]⁴⁻ tetrahedra that are connected only by interstitial cations. Nickel–Strunz classification: 09.A

Examples are:

• Phenakite group
  • Phenakite – Be₂SiO₄
  • Willemite – Zn₂SiO₄
• Olivine group
  • Forsterite – Mg₂SiO₄
  • Fayalite – Fe₂SiO₄
  • Tephroite – Mn₂SiO₄
• Garnet group
  • Pyrope – Mg₃Al₂(SiO₄)₃
  • Almandine – Fe₃Al₂(SiO₄)₃
  • Spessartine – Mn₃Al₂(SiO₄)₃
  • Grossular – Ca₃Al₂(SiO₄)₃
  • Andradite – Ca₃Fe₂(SiO₄)₃
  • Uvarovite – Ca₃Cr₂(SiO₄)₃
  • Hydrogrossular – Ca₃Al₂Si₂O₈(SiO₄)_3−m(OH)_4m
• Zircon group
  • Zircon – ZrSiO₄
  • Thorite – (Th,U)SiO₄
  • Hafnon – (Hf,Zr)SiO₄

Kyanite crystals (unknown scale)

• Al₂SiO₅ group
  • Andalusite – Al₂SiO₅
  • Kyanite – Al₂SiO₅
  • Sillimanite – Al₂SiO₅
  • Dumortierite – Al_6.5–7BO₃(SiO₄)₃(O,OH)₃
  • Topaz – Al₂SiO₄(F,OH)₂
  • Staurolite – Fe₂Al₉(SiO₄)₄(O,OH)₂
• Humite group – (Mg,Fe)₇(SiO₄)₃(F,OH)₂
  • Norbergite – Mg₃(SiO₄)(F,OH)₂
  • Chondrodite – Mg₅(SiO₄)₂(F,OH)₂
  • Humite – Mg₇(SiO₄)₃(F,OH)₂
  • Clinohumite – Mg₉(SiO₄)₄(F,OH)₂
• Datolite – CaBSiO₄(OH)
• Titanite – CaTiSiO₅
• Chloritoid – (Fe,Mg,Mn)₂Al₄Si₂O₁₀(OH)₄
• Mullite (aka Porcelainite) – Al₆Si₂O₁₃

Sorosilicates

Sorosilicate exhibit at Museum of Geology in South Dakota

Sorosilicates (from Greek σωρός sōros, heap, mound) have isolated double tetrahedra groups with (Si₂O₇)⁶⁻ or a ratio of 2:7. Nickel–Strunz classification: 09.B

Examples are:

• Hemimorphite (calamine) – Zn₄(Si₂O₇)(OH)₂·H₂O
• Lawsonite – CaAl₂(Si₂O₇)(OH)₂·H₂O
• Axinite – (Ca,Fe,Mn)₃Al₂(BO₃)(Si₄O₁₂)(OH)
• Ilvaite – CaFe^II₂Fe^IIIO(Si₂O₇)(OH)
• Epidote group (has both (SiO₄)⁴⁻ and (Si₂O₇)⁶⁻ groups)
  • Epidote – Ca₂(Al,Fe)₃O(SiO₄)(Si₂O₇)(OH)
  • Zoisite – Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
    • Tanzanite – Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
  • Clinozoisite – Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
  • Allanite – Ca(Ce,La,Y,Ca)Al₂(Fe^II,Fe^III)O(SiO₄)(Si₂O₇)(OH)
  • Dollaseite-(Ce) – CaCeMg₂AlSi₃O₁₁F(OH)
• Vesuvianite (idocrase) – Ca₁₀(Mg,Fe)₂Al₄(SiO₄)₅(Si₂O₇)₂(OH)₄

Cyclosilicates

Cyclosilicate specimens at the Museum of Geology, South Dakota

Cyclosilicates (from Greek κύκλος kuklos, circle), or ring silicates, have linked tetrahedra with (T_xO_3x)^2x− or a ratio of 1:3. These exist as 3-member (T₃O₉)⁶⁻ and 6-member (T₆O₁₈)¹²⁻ rings, where T stands for a tetrahedrally coordinated cation. Nickel–Strunz classification: 09.C

Examples are:

• 3-member ring
  • Benitoite – BaTi(Si₃O₉)
• 6-member ring
  • Beryl – Be₃Al₂(Si₆O₁₈)
  • Bazzite – Be₃Sc₂(Si₆O₁₈)
  • Sugilite – KNa₂(Fe,Mn,Al)₂Li₃Si₁₂O₃₀
  • Tourmaline – (Na,Ca)(Al,Li,Mg)₃₋(Al,Fe,Mn)₆(Si₆O₁₈(BO₃)₃(OH)₄
  • Pezzottaite – Cs(Be₂Li)Al₂Si₆O₁₈
  • Milarite – K₂Ca₄Al₂Be₄(Si₂₄O₆₀)H₂O
  • Osumilite – (K,Na)(Fe,Mg)₂(Al,Fe)₃(Si,Al)₁₂O₃₀
  • Cordierite – (Mg, Fe)₂Al₄Si₅O₁₈
  • Sekaninaite – (Fe⁺², Mg)₂Al₄Si₅O₁₈

Note that the ring in axinite contains two B and four Si tetrahedra and is highly distorted compared to the other 6-member ring cyclosilicates.

• 
  Cyclosilicate, [Si₆O₁₈] – 6-membered single rings, beryl (red: Si, blue: O)
• 
  Cyclosilicate, [Si₃O₉] – 3-membered single ring, benitoite
• 
  Cyclosilicate, [Si₄O₁₂] – 4-membered single ring, papagoite
• 
  Cyclosilicate, [Si₉O₂₇] – 9-membered ring, eudialyte
• 
  Cyclosilicate, [Si₆O₁₈] – 6-membered double ring, milarite
• 
  Pezzottaite
• 
  Bazzite

Inosilicates

Inosilicates (from Greek ἴς is [genitive: ἰνός inos], fibre), or chain silicates, have interlocking chains of silicate tetrahedra with either SiO₃, 1:3 ratio, for single chains or Si₄O₁₁, 4:11 ratio, for double chains. Nickel–Strunz classification: 09.D

Examples are:

Single chain inosilicates

• Pyroxene group
  • Enstatite – orthoferrosilite series
    • Enstatite – MgSiO₃
    • Ferrosilite – FeSiO₃
  • Pigeonite – Ca_0.25(Mg,Fe)_1.75Si₂O₆
  • Diopside – hedenbergite series
    • Diopside – CaMgSi₂O₆
    • Hedenbergite – CaFeSi₂O₆
    • Augite – (Ca,Na)(Mg,Fe,Al)(Si,Al)₂O₆
  • Sodium pyroxene series
    • Jadeite – NaAlSi₂O₆
    • Aegirine (Acmite) – NaFe^IIISi₂O₆
  • Spodumene – LiAlSi₂O₆
• Pyroxenoid group
  • Wollastonite – CaSiO₃
  • Rhodonite – MnSiO₃
  • Pectolite – NaCa₂(Si₃O₈)(OH)

Double chain inosilicates

• Amphibole group
  • Anthophyllite – (Mg,Fe)₇Si₈O₂₂(OH)₂
  • Cummingtonite series
    • Cummingtonite – Fe₂Mg₅Si₈O₂₂(OH)₂
    • Grunerite – Fe₇Si₈O₂₂(OH)₂
  • Tremolite series
    • Tremolite – Ca₂Mg₅Si₈O₂₂(OH)₂
    • Actinolite – Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂
  • Hornblende – (Ca,Na)_2–3(Mg,Fe,Al)₅Si₆(Al,Si)₂O₂₂(OH)₂
  • Sodium amphibole group
    • Glaucophane – Na₂Mg₃Al₂Si₈O₂₂(OH)₂
    • Riebeckite (asbestos) – Na₂Fe^II₃Fe^III₂Si₈O₂₂(OH)₂
    • Arfvedsonite – Na₃(Fe,Mg)₄FeSi₈O₂₂(OH)₂

• 
  Inosilicate, pyroxene family, with 2-periodic single chain (Si₂O₆), diopside
• 
  Inosilicate, clinoamphibole, with 2-periodic double chains (Si₄O₁₁), tremolite
• 
  Inosilicate, unbranched 3-periodic single chain of wollastonite
• 
  Inosilicate with 5-periodic single chain, rhodonite
• 
  Inosilicate with cyclic branched 8-periodic chain, pellyite

Phyllosilicates

Phyllosilicates (from Greek φύλλον phyllon, leaf), or sheet silicates, form parallel sheets of silicate tetrahedra with Si₂O₅ or a 2:5 ratio. Nickel–Strunz classification: 09.E. All phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached.

Kaolinite

Examples are:

• Serpentine subgroup
  • Antigorite – Mg₃Si₂O₅(OH)₄
  • Chrysotile – Mg₃Si₂O₅(OH)₄
  • Lizardite – Mg₃Si₂O₅(OH)₄
• Clay minerals group
  • Halloysite – Al₂Si₂O₅(OH)₄
  • Kaolinite – Al₂Si₂O₅(OH)₄
  • Illite – (K,H₃O)(Al,Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O)]
  • Montmorillonite – (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O
  • Vermiculite – (MgFe,Al)₃(Al,Si)₄O₁₀(OH)₂·4H₂O
  • Talc – Mg₃Si₄O₁₀(OH)₂
  • Sepiolite – Mg₄Si₆O₁₅(OH)₂·6H₂O
  • Palygorskite (or attapulgite) – (Mg,Al)₂Si₄O₁₀(OH)·4(H₂O)
  • Pyrophyllite – Al₂Si₄O₁₀(OH)₂
• Mica group
  • Biotite – K(Mg,Fe)₃(AlSi₃)O₁₀(OH)₂
  • Fuchsite – K(Al,Cr)₂(AlSi₃O₁₀)(OH)₂
  • Muscovite – KAl₂(AlSi₃)O₁₀(OH)₂
  • Phlogopite – KMg₃(AlSi₃)O₁₀(OH)₂
  • Lepidolite – K(Li,Al)_2–3(AlSi₃)O₁₀(OH)₂
  • Margarite – CaAl₂(Al₂Si₂)O₁₀(OH)₂
  • Glauconite – (K,Na)(Al,Mg,Fe)₂(Si,Al)₄O₁₀(OH)₂
• Chlorite group
  • Chlorite – (Mg,Fe)₃(Si,Al)₄O₁₀(OH)₂·(Mg,Fe)₃(OH)₆

• 
  Phyllosilicate, mica group, muscovite (red: Si, blue: O)
• 
  Phyllosilicate, single net of tetrahedra with 4-membered rings, apophyllite-(KF)-apophyllite-(KOH) series
• 
  Phyllosilicate, single tetrahedral nets of 6-membered rings, pyrosmalite-(Fe)-pyrosmalite-(Mn) series
• 
  Phyllosilicate, single tetrahedral nets of 6-membered rings, zeophyllite
• 
  Phyllosilicate, double nets with 4- and 6-membered rings, carletonite

Tectosilicates

Tectosilicates, or "framework silicates," have a three-dimensional framework of silicate tetrahedra with SiO₂ or a 1:2 ratio. This group comprises nearly 75% of the crust of the Earth. Tectosilicates, with the exception of the quartz group, are aluminosilicates. Nickel–Strunz classification: 09.F and 09.G, 04.DA (Quartz/ silica family)

Quartz

Lunar ferroan anorthosite (plagioclase feldspar) collected by Apollo 16 astronauts from the Lunar Highlands near Descartes Crater

Examples are:

• Quartz group
  • Quartz – SiO₂
  • Tridymite – SiO₂
  • Cristobalite – SiO₂
  • Coesite – SiO₂
  • Stishovite – SiO₂
  • Moganite – SiO₂
  • Chalcedony – SiO₂
• Feldspar family
  • Alkali feldspars (potassium feldspars)
    • Microcline – KAlSi₃O₈
    • Orthoclase – KAlSi₃O₈
    • Anorthoclase – (Na,K)AlSi₃O₈
    • Sanidine – KAlSi₃O₈
  • Plagioclase feldspars
    • Albite – NaAlSi₃O₈
    • Oligoclase – (Na,Ca)(Si,Al)₄O₈     (Na:Ca 4:1)
    • Andesine – (Na,Ca)(Si,Al)₄O₈     (Na:Ca 3:2)
    • Labradorite – (Ca,Na)(Si,Al)₄O₈     (Na:Ca 2:3)
    • Bytownite – (Ca,Na)(Si,Al)₄O₈     (Na:Ca 1:4)
    • Anorthite – CaAl₂Si₂O₈
• Feldspathoid family
  • Nosean – Na₈Al₆Si₆O₂₄(SO₄)
  • Cancrinite – Na₆Ca₂(CO₃,Al₆Si₆O₂₄).2H₂O
  • Leucite – KAlSi₂O₆
  • Nepheline – (Na,K)AlSiO₄
  • Sodalite – Na₈(AlSiO₄)₆Cl₂
    • Hauyne – (Na,Ca)_4–8Al₆Si₆(O,S)24(SO₄,Cl)_1–2
  • Lazurite – (Na,Ca)₈(AlSiO₄)₆(SO₄,S,Cl)₂
• Petalite – LiAlSi₄O₁₀
• Scapolite group
  • Marialite – Na₄(AlSi₃O₈)₃(Cl₂,CO₃,SO₄)
  • Meionite – Ca₄(Al₂Si₂O₈)₃(Cl₂CO₃,SO₄)
• Analcime – NaAlSi₂O₆·H₂O
• Zeolite family
  • Natrolite – Na₂Al₂Si₃O₁₀·2H₂O
  • Erionite – (Na₂,K₂,Ca)₂Al₄Si₁₄O₃₆·15H₂O
  • Chabazite – CaAl₂Si₄O₁₂·6H₂O
  • Heulandite – CaAl₂Si₇O₁₈·6H₂O
  • Stilbite – NaCa₂Al₅Si₁₃O₃₆·17H₂O
  • Scolecite – CaAl₂Si₃O₁₀·3H₂O
  • Mordenite – (Ca,Na₂,K₂)Al₂Si₁₀O₂₄·7H₂O

Gallery

• 
  Nesosilicate (SiO₄)
• 
  Sorosilicate (Si₂O₇), as in suolunite
  [Ca₂Si₂O₅(OH)₂·H₂O
• 
  Tectosilicate, aluminosilicate 3D network, zeolite family, synthetic zeolite ZSM-5
• 
  Silica family (SiO₂ 3D network), β-quartz

See also

• Classification of non-silicate minerals
• Classification of silicate minerals
• Silicate mineral paint

Further references

• Deer, W.A.; Howie, R.A.; Zussman, J. (1992). An introduction to the rock-forming minerals (2nd ed.). London: Longman. ISBN 0-582-30094-0. 

• Deer, W.A.; Howie, R.A.; Wise, W.S.; Zussman, J. (2004). Rock-forming minerals. Volume 4B. Framework silicates: silica minerals. Feldspathoids and the zeolites (2nd ed.). London: Geological Society of London. p. 982 pp. 

• Hurlbut, Cornelius S. (1966). Dana's Manual of Mineralogy (17th ed.). ISBN 0-471-03288-3. 

• Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). Wiley. ISBN 0-471-80580-7. 

• Mindat.org, Dana classification
• Webmineral : Dana's New Silicate Classification

External links

The Wikibook Historical Geology has a page on the topic of: Silicate minerals

Media related to Silicates at Wikimedia Commons